Ziegler discovered a two component catalyst for the polymerization of olefins. The catalyst included a compound of the group IVB-VIB metals of the periodic table and an organometallic compound belonging to Groups I-IIIA of the periodic table. The traditional Ziegler catalysts efficiently promoted the polymerization and copolymerization of olefins to provide high yields of polyolefins that possess the properties desired for practical applications. However, although Ziegler catalysts have been widely utilized, conventional Ziegler catalysts demonstrate important disadvantages. Researchers have discovered numerous Ziegler-type catalysts that demonstrated improvements over the traditional Ziegler catalysts. The improved Ziegler-type catalysts have been employed for many years in the production of polyolefins. However, these new catalysts had relatively low activity and stability. Thus, because disadvantages in Ziegler-type catalysts still exist, improvements in Ziegler-type catalysts for polymerizing one or more 1-olefins are continually being sought.
Researchers especially have attempted to provide catalysts demonstrating a higher activity and a high stereospecificity. In particular, so-called "supported catalysts", such as titanium supported on a suitable carrier, have been developed. For example, U.S. Pat. No. 2,981,725 discloses a process wherein the catalyst components were deposited on an inert support such as magnesium chloride, silicon carbide, silica gel, calcium chloride or a similar compound. However, the activity of the resulting catalyst is still low. In addition, several catalysts have been disclosed wherein a titanium halide or a vanadium halide is reacted with a magnesium-containing support, such as a magnesium alkoxide or magnesium hydroxy chloride. U.S. Pat. Nos. 3,654,249; 3,759,884; 4,039,472; 4,082,692; and 4,097,409 describe such catalysts. These supported catalysts greatly increased the ability of the titanium to polymerize a 1-olefin compared to a traditional Ziegler catalyst.
Research has been directed to making improved supported catalysts. Numerous patents disclose catalysts supported on silica or alumina. Porous silica and alumina supports for high-reactivity catalysts were found to fracture during polymerization reactions. The residual, fractured particles of catalyst in the polyolefins were sufficiently small such that the particles did not adversely affect the polyolefins. In contrast, nonporous silica and alumina catalyst supports do not fracture during polymerization reactions. Therefore, the residual nonporous catalyst particles embedded in the polyolefin resins were sufficiently large to cause bubble tearing in blown film line operations; defects and gels in thin films; and clogged filters in extruders.
Other support materials for Ziegler-type catalysts have been sought. For example, U.S. Pat. Nos. 3,297,466 and 3,503,785 disclose that solid particles, such as cellulose, carbon black, wool, silk, asbestos, glass fibers, metals, oxides and synthetic fibers, can be encapsulated by polymerizing an olefin on a solid particle surface having a polymerization catalyst incorporated therein. U.S. Pat. No. 3,121,658 discloses treating cellulose fibers with a two-component Ziegler catalyst to catalyze the polymerization of ethylene or propylene on the fiber, and therefore encapsulate the cellulose fiber. Marchessault et al., in U.S. Pat. No. 3,926,717, disclose forming a Ziegler-type catalyst throughout a formed cellulosic substrate. An olefin then is polymerized throughout the cellulosic substrate to improve the water resistance and heat-sealing properties of the substrate.
Other patents and publications also disclosed forming a Ziegler-type catalyst on a cellulosic substrate. For example, Kaminsky, in "Polymerization and Copolymerization with a Highly Active, Soluble Ziegler-Natta Catalyst", Transition Metal Catalyzed Polymerization, Alkenes and Dienes, Part A, R. P. Quirk, et al., eds., Harwood Academic Publishers, pp. 225-244 (1981), discloses coating a surface of a cellulosic substrate with a polymer by attaching a catalyst to the surface of the substrate, then polymerizing ethylene on the substrate surface. Other patents and publications that disclose the use of a cellulosic substrate for a Ziegler-type catalyst include:
H. D. Chanzy, "Transition Metal Catalysts for Polyethylene Encapsulation of Substrates", Ph.D. Thesis, Syracuse University (1966);
A. Dankovics et al., J. Appl. Poly. Sci., Vol. 13, pp. 1809-1824 (1969), wherein a Ziegler-Natta catalyst is adsorbed onto a cellulose surface, and a subsequent polymerization of propylene on the surface encapsulates the cellulose, the encapsulated cellulose and untreated cellulose then are combined to form a pulp to make paper;
Dougherty, U.S. Pat. No. 4,012,342, discloses the low pressure polymerization of olefins on the surface of organic fibers including a catalyst to provide a high molecular weight polymer;
Kochhar et al., U.S. Pat. No. 4,021,599; Beach et al., U.S. Pat. No. 4,329,255; UK Patent No. 834,217; Calvert et al., U.S. Pat. No. 3,876,602; Fulks et al., U.S. Pat. Nos. 4,532,311 and 4,792,592; and Goode et al., U.S. Pat. No. 4,803,251. None of these patents or publications disclose the catalyst and methods of the invention. Although these later investigations extended the original work of Ziegler to produce several improved catalysts, no catalyst has exhibited the improved properties demonstrated by a catalyst of the invention.
In general, some of the above-identified patents and publications disclose a traditional Ziegler catalyst made from two components. These original Ziegler catalysts were characterized by a low reactivity compared to later Ziegler-type catalysts. The improved Ziegler-type catalysts were higher activity catalysts formed on the surface of a solid inorganic support from an organometallic compound and a transition metal compound. The resulting Ziegler-type catalyst then was used in a polymerization reaction with a cocatalyst, like an alkyl-aluminum compound. Isotacticity promoters and reactivity promoters also can be included in the polymerization reaction.
Ziegler catalysts that utilized a solid organic support, such as cellulose, were traditional Ziegler catalysts that merely provided a sufficient amount of polymer to coat or encapsulate the organic support. In contrast to merely encapsulating the organic support, a catalyst of the present invention is an improved Ziegler-type catalyst and provides extensive polymerization at the internal and external surfaces of the organic support. The polymerization is sufficiently extensive that the organic support particles are fragmented by the growing polymer. This particle fragmentation provides an intimate molecular level blending of the organic support material with the polyolefin.
The prior art has addressed some of the features demonstrated by a catalyst of the invention. However, the prior art catalysts for polymerizing 1-olefins still possessed disadvantages. For example, in the polymerization of 1-olefins, the presence of residual catalyst in the polymer product can cause corrosion in molding machines and can introduce esthetic flaws into the molded polymer product. Accordingly, the catalyst residue was stripped from the polymer product before molding. Therefore, it would be advantageous to provide a catalyst for polymerizing 1-olefins that can remain in the polymer product and not adversely affect the molding apparatus or the esthetic properties of the molded product. Such a catalyst would eliminate a costly and time-consuming step in the processing of polymerized 1-olefins.
Furthermore, researchers have attempted to discover a polymer that possesses the desirable physical and chemical properties of a polymerized 1-olefin, and that also is biodegradable. Attempts at incorporating the feature of biodegradability into a poly-1-olefin either have failed or have adversely affected the physical properties of the polymer. Therefore, it also would be advantageous to utilize a polymerization catalyst that incorporates a degree of biodegradability into a poly-1-olefin. It would be especially advantageous if the catalyst could impart the feature of biodegradability, or pseudobiodegradability, into the poly-1-olefin product because the need for biodegradable additives, or for comonomers, to promote biodegradability of the polymer would be eliminated. Consequently, the full benefits of the desirable physical and chemical properties of a poly-1-olefin could be realized. No known catalyst useful for homopolymerizing or copolymerizing 1-olefins meets this need for imparting biodegradability into the polymer.
For example, physically blending starch and polyethylene provides a mixture exhibiting a degree of biodegradability. However, in accordance with the invention, the biodegradable component is included in the catalyst, and in accordance with another important feature of the invention, the biodegradable component is more uniformly and intimately dispersed throughout the poly-1-olefin, and the amount of the biodegradable component included in the poly-1-olefin is reduced while maintaining the same degree of biodegradability.